The present invention relates to a lithography method and a lithography system using a charged particle beam, and more particularly, to a lithography method and system in which a photoresist film is irradiated with light while the charged particle beam is applied. More specifically, the present invention is applied to a character projection method and system for a mask pattern using an electron beam.
Recently, in a photolithography technology for LSI, shorter-wavelength light has been increasingly used for obtaining a micro pattern. Furthermore, lithographic techniques using a charged particle beam and X-rays have been proposed to attain a direct writing of the micro pattern.
FIG. 1 is a schematic view of a conventional lithography system using an electron beam. The system shown in FIG. 1 comprises a thermal cathode 401, a wehnelt electrode 402, an aperture 403 having a rectangular opening for shaping a beam, a first beam-shaping electron lens 404, a beam deflector 405, a second beam-shaping electron lens 406, a mask stage 407, a transfer mask 408 mounted on the mask stage, a demagnification lens 409, an objective lens 410, a beam deflector 411, a wafer stage 413, and a wafer 412 mounted on the wafer stage and having a photoresist film coated on the upper surface thereof.
In the lithography system having the aforementioned structure, electrons emitted from an electron gun, which is composed of the thermal cathode 401 and the wehnelt electrode 402, are allowed to pass through the aperture 403 to form a rectangular beam. Furthermore, the electron beam is applied onto the transfer mask 408 by the function of the beam-shaping electron lenses 404 and 406. At this time, by using the beams deflector 405 interposed between the beams shaping electron lenses 404 and 406, an arbitrarily chosen position on the transfer mask 408 can be irradiated. The transfer mask 408 has an opening portion whose shape is obtained by synthesizing a rectangular and an ellipse. Therefore, if the opening portion on the transfer mask 408 is irradiated with the rectangular shaped beam, the resultant beam is obtained in a desired shape.
In addition, owing to the functions of the beam deflector 405 and the mask stage 407, the electron beam can be applied to an arbitrarily chosen cell pattern portion within the transfer mask 408.
The electron beam passed through the transfer mask 408 is demagnified and projected onto the wafer 412 by means of the demagnification lens 409 and the object lens 411, and then applied to the photoresist film coated on the wafer 412. In this case, the entire surface of the wafer 412 can be irradiated by combining beam deflection by the beam deflector 411 with the movement of the wafer 412 by the wafer stage 413.
According to the direct writing technique on the wafer performed by using the electron-beam lithography system, a micro pattern of 0.2 .mu.m or less can be formed.
However, the direct writing technique on the wafer has problems. The most significant problem is a low productivity. To describe more specifically, the throughput of wafer in the pattern exposure step is low. This is because, in the direct writing technique, a desired beam shape is obtained by applying the rectangular beam to the opening portion of the transfer mask, so that writing has to be made by dividing all patterns to be written in accordance with the rectangular beam shapes. In this method, even if repetition patterns are employed, the patterns are divided and then writing is made. As a result, the number of beam shots drastically increases. It is therefore impossible to improve the throughput. To improve this problem, recently proposed is a cell projection method in which an image of a repetition pattern previously formed on the transfer mask, is transferred onto the wafer. This method suggests the possibility of the high-speed writing using the electron beam.
When pattern exposure of a semiconductor memory is performed by using the electron beam, if the cell array portion is written by the cell projection method (since the cell array portion has a repeat pattern) and the peripheral circuit portion is written by a variable shaped beam varied in shape and size, the number of beam shots can be drastically reduced. As a result, high-speed writing can be attained.
However, even if the aforementioned high speed writing method is used, a beam shot density comes up to 10.sup.4 to 10.sup.5 shots/mm.sup.2. Therefore, the shot number (density) will restrict the throughput of the wafer. Since the size of the beam shot is determined by characteristics of the electron beam optical system in the lithography system, the low throughput inevitably occurs in the case where the pattern on the transfer mask is demagnified and projected.
On the other hand, as a micro patterning technique more suitable than the optical lithography, X-ray lithography is known. The X-ray lithography has many advantages including linearity and non-interference, over the conventionally-used lithography using visible light and ultraviolet light. However, it has a problem of a low throughput due to a low photosensitivity of resist, difficulty in alignment, and difficulty in mask material selection and in processing thereof.
To solve the low sensitivity of a resist in the X-ray lithography, proposed is a method for increasing an effective sensitivity of the resist by use of a secondary radiation from the fluorescent film (Japanese Patent Application KOKAI Publication No. 63-53922). In this method, since the fluorescent material layer is arranged above the mask material holding thin film (on the X-ray source side), the sensitivity of the resist for X-rays can be auxiliarily increased by application of the secondary radiation generated from the fluorescent material layer. However, the X-ray lithography has many problems to be solved, such as a cost, safety of the X-ray source and an improvement of productivity.